Infectious diseases remain a major cause of morbidity and mortality worldwide. According to the who. in Africa alone from malaria suffer from 100 million people. Here are a few “new” reasons for which infectious disease in recent years attracted more and more attention:
- Identified new pathogens that cause diseases such as Legionnaires ‘ disease, acquired immunodeficiency syndrome;
- Increasingly, States that the clinical course of “old” infectious diseases does not fit the classic clinical picture;
- Increasing the number of patients in which there is a secondary immunodeficiency caused by iatrogenic causes, which is a risk factor for the development of their “opportunistic” infections;
- It is established that an atypical immune response to the microorganisms, in some cases, is the cause of the development of somatic autoimmune pathology;
- An important reason for the increased attention to infections are the increased contacts between countries through air transport, which increases the possibility of “sharing” region-specific pathogens.
It should be noted that historically the development of immunology began with the study of immune defense. It is now clearly proved that the susceptibility of humans and animals to various types of infectious agents varies and has a significant individual differences, which depends both on the pathogen and host.
On the part of the pathogen are important, first of all:
- The infectious dose;
- The entrance gate of the infectious agent;
- The virulence of the pathogen.
By “host” factors determining the possibility of development of infectious diseases are:
- Coherence (integration) in the nonspecific defense factors (factors natural, innate, immunity);
- The normal functioning of specific, adaptive immunity;
- Individual immunogenetic features recognition of specific pathogen and immune cells of the host.
All the human body systems, including immune, evolved in constant interaction with microorganisms inhabiting in the environment. In turn, the microorganisms also have evolved and adapted to the optimum to exist in the human body using its reserves for their livelihoods.
This has resulted in several types of interaction between micro – and macroorganism, the main ones being antagonistic and synergistic.
Antagonistic interaction leads to the development of the infectious process, and synergy as due to the existence in the human body mainly in the gut, skin and respiratory tract, and conditionally pathogenic microorganisms. However, the latter may contribute to the development of infection while reducing the overall resistance of the organism or when infected with a high dose of pathogens that is accompanied by the formation of primary purulent focus – producer of substances that determine the occurrence, course and outcome of infection.
Finally, another important type of interaction of human body with microorganisms is cooperation with the so-called normal microflora and the formation of colonization resistance.
Normal human microflora includes hundreds of species, mainly obligate anaerobic bacteria that form on various parts of the skin and mucous membranes of the microbial associations that prevent colonization of host others, including pathogenic microorganisms. The number of representatives of normal human microflora reaches 1014, while the total number of body cells to about 1013 i.e. one host cell practically have 10 units of normal microflora. Range of microbiocenosis of man determined by the peculiarities of its metabolism, biochemical and antigenic composition of the tissues of the nervous, immune and endocrine systems.
For its part, the normal microflora influences the tissue morphogenesis, metabolism of carbohydrates, lipids, hormones, salt metabolism, the formation of mutagens and antimutagenic agents in the host organism.
As already mentioned, one of the most important factors determining the development of infectious diseases is the immune system of a person, her innate nonspecific defense factors and specific adaptive immunity. In the respective chapters of the present book is a detailed description of the structure and mechanisms of differentiation of these two systems. Briefly recall them taking into account the specifics of this Chapter.